Gamma-ray bursts' highest power side unveiled by Fermi telescope

Feb 19, 2012

(PhysOrg.com) -- Detectable for only a few seconds but possessing enormous energy, gamma-ray bursts are difficult to capture because their energy does not penetrate the Earth's atmosphere. Now, thanks to an orbiting telescope, astrophysicists are filling in the unknowns surrounding these bursts and uncovering new questions.

The Fermi Gamma-Ray Space Telescope, formerly called the Gamma-Ray Large Area Space Telescope, launched on June 11, 2008. As part of its mission, the telescope records any gamma-ray bursts within its viewing area.

"Fermi is lucky to measure the highest energy portion of the gamma-ray burst emission, which last for hundreds to thousands of seconds -- maybe 20 minutes," said Péter Mészáros, Eberly Chair Professor of Astronomy and Astrophysics and Physics, Penn State.

Most gamma-ray bursts occur when stars that are more than 25 times larger than our sun come to the end of their lives. When the internal nuclear reaction in these stars ends, the star collapses in on itself and forms a black hole. The outer envelope of the star is ejected forming a supernova.

"The black hole is rotating rapidly and as it is swallowing the matter from the star, the rotation ejects a jet of material through the supernova envelope," said Mészáros.

This jet causes the gamma-ray burst, which briefly becomes the brightest thing in the sky. However, unlike supernovas that radiate in all directions, gamma-ray bursts radiate in a very narrow area, and Fermi sees only jets ejecting in its direction. This, however, is the direction in which they send their highest energy photons. Any gamma-ray bursts on the other side of the black hole or even off at an angle are invisible to the telescope.

"We actually miss about 500 gamma-ray bursts for every one we detect," Mészáros told attendees today at the annual meeting of the American Association for the Advancement of Science in Vancouver, British Columbia.

The gamma-ray bursts that Fermi has seen have allowed astrophysicists to clarify previous theories about gamma-ray bursts.

"We have been able to rule out the simplest version of theories which combine quantum mechanics with gravity, although others remain to be tested," said Mészáros.

Mészáros notes that Fermi and other programs like the SWIFT telescope have shown that gamma-ray bursts last longer than we thought they did and that there are long and short gamma-ray bursts.

Fermi, a more specialized telescope than the SWIFT telescope which also detects gamma-ray bursts, enabled scientists to look at the very fast -- near the speed of light -- jets producing the gamma-ray emissions. While researchers are still modifying scientific theories on the nature of these bursts, thanks to Fermi, they now have actual measurements to add to the theoretical debate.

"Fermi has done much better in measuring how close to the speed of light the jet gets," said Mészáros. "But we still don't know if it is 99.9995 percent the speed of light or 99.99995 percent the speed of light."

Gamma-ray bursts occur in many places in the universe, but because they are a product of aging stars they may be able to shed some light on the beginnings of the universe. The bursts are visible at the longest distance from earth and therefore at the earliest time in the universe.

"We think we can detect them at the infancy of the universe," said Mészáros.

Wherever a gamma-ray burst exists, any planets in the vicinity suffer. Further away, the radiation from a gamma-ray burst would destroy the protective ozone in the upper atmosphere, allowing ultraviolet radiation to kill terrestrial plant life and animals would starve. Only sea life would remain unharmed. However, it is estimated that such nearby bursts can be expected only every 300 million years.

Because scientists believe that gamma-ray bursts also emit cosmic rays and neutrinos, other observatories are also observing these phenomena. Ice Cube Neutrino Observatory at the South Pole is trying to capture neutrinos, while the Pierre Auger Cosmic Ray Observatory in Argentina captures cosmic rays from these objects.

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You have meant probably this one. http://www.nasa.g...527.html You're right, such early GRB's pose a stress to Big Bang theory, because in this model the first hydrogen and helium from the Big Bang condensed into the first stars 500 million years after the Big Bang. http://en.wikiped...ynthesis Dense aether model of steady state Universe has no problem with such observations, because it considers, these stars were already formed in normal functioning galaxies. There is additional problem with the observability of such distant GRB's, which apparently do violate the GZK limit (a cosmic ray paradox). http://en.wikiped...in_limit It should be pointed out, dense aether model is solving it too with gravitational mass of gamma ray photons involved.

@ant phy: Whoops, I missed it by a set of three more zeros. It is GRB 090423 at 630 million ly's from BB/Inflation, z=8.2. Interesting to compare that redshift to that of HUDF-JD2 which is at 800 million with redshift between 6 & 7.

@Cal: You're right, I got the two mixed up. I was sure there was one at about 500 million. This brings the redshift at around z=9.2 for 090429B.

Supernovae are caused at the moment iron starts to form in the core. The point I'm trying to make here: this is associated only with extreme aging of stars, a lot older than 520 million years from BB/Inflation. This why I continue to suggest Cosmologists have got to rethink the 13.7 billion year age of BB/Inflation.

I remember reading about a GRB that was detected at 500,000 years from the BB/Inflation.

That GRBs can originate from dying stars does not mean that ALL GRBs originate from dying stars.

Two stars, or even gas fronts, colliding could also produce one - and that much earlier than when the first stars start to burn out.

Add to that that we don't really know what role dark matter played in the early universe. It does have a gravitational effect, so the temperature/gas pressure could have been overcome by gravity to form stars earlier.

because in this model the first hydrogen and helium from the Big Bang condensed into the first stars 500 million years after the Big Bang

I think you have your numbers wrong on this. The current model puts first star formation at the 100 million years (some at 30 million years).

You're right, such early GRB's pose a stress to Big Bang theory, because in this model the first hydrogen and helium from the Big Bang condensed into the first stars 500 million years after the Big Bang.

Hydrogen (and helium) formed about 300-400K years after the BB. By 500 million years the first generation of massive stars were already gone as supernovae. If we stress the model to it's absolute limits, 100 (ok, maybe 10-15) genereations of massive stars could have been born, burned out and exploded in that timeframe.

The point I'm trying to make here: this is associated only with extreme aging of stars, a lot older than 520 million years from BB/Inflation.

Benni: please don't forget that some stars, the massive ones, live only like 3-30 million years. By that time they are considered "extreme aged" and are on the verge of death, trying to support an earth sized iron core.

You're right, such early GRB's pose a stress to Big Bang theory, because in this model the first hydrogen and helium from the Big Bang condensed into the first stars 500 million years after the Big Bang.

Hydrogen (and helium) formed about 300-400K years after the BB. By 500 million years the first generation of massive stars were already gone as supernovae. If we stress the model to it's absolute limits, 100 (ok, maybe 10-15) genereations of massive stars could have been born, burned out and exploded in that timeframe.

.....but only if they've begun the transition to iron in the core can they supernovae. What I'm trying to get a feel for is the absolute minimum time a star must exist before this can occur. I've searched & can't find anything specifically on this point.

The point I'm trying to make here: this is associated only with extreme aging of stars, a lot older than 520 million years from BB/Inflation.

Benni: please don't forget that some stars, the massive ones, live only like 3-30 million years. By that time they are considered "extreme aged" and are on the verge of death, trying to support an earth sized iron core.

Fair point.....but ultimately what I'm hoping to discover is if the fusion process can accelerate to iron in only 3-30-100 million years. I pretty well understand the fission process from a course I had in nuclear reactor design but fusion is something I've had to pretty much pick up on my own. Fusion inside of stars to iron was a process I had assumed would run into the billions of years.... still need help here.

.....but only if they've begun the transition to iron in the core can they supernovae

Iron in the core is not a prerequisite for a supernova. E.g. white dwarf stars can go supernova while still only having gotten up to carbon in the core (Type Ia supernova).

In huge stars the conversion isn't a straight sequence. It's not "only hydrogen fusion, then only helium fusion, ..."The types start up one after another but can then be ongoing all at the same time (in different depths of the star)

This link contains a table for the durations of a 25 solar mass star. As you can see it goes through the entire cycle in about 11 million years (the bigger a star the shorter its lifespan). Upper limit for stars seems to be 120 solar masses. These suckers would go through their lifecycle quite a bit faster.

Seem to remember that the highest terrestrially monitored cosmic ray energy was twenty joule - would have liked it if this report had given some idea of the power spectrum measured by the space-based gamma-ray telescope. One wonders what background cosmic radiation has contributed to phylogenetic genomic variation due to mutational effects, although self-repair in organisms is evident. Micrococcus radiodurans exposed to 220 keV X-rays at a dose rate of 11 kilorads per minute, shows that no cell inactivation occurs at doses up to 0.5 Mrad, and 37% of the cells survive after 0.8 Megarad.

Interesting. I see the table is Solar Mass specific at the six levels of the onion. I have seen that diagram before but not with the table indicating time durations as the collapse moves from layer to layer. Now I need to find a table that tracks multiple solar masses, not just 25.

Hey, you posted right before me on the "transistor" news. Are these guys good or what?

Whilst the early supernovae were probably pair instability types rather than Type I or II, it is worth noting that the speed of the fusion reactions goes up as the temperature and pressure in the core of large stars increases. The stage from silicon to iron may take only about a day. When the iron core reaches the point of collapse into neutrons the surface falls in at speeds of ~0.2c. This is all happening very fast!For Type Ia once the Chandrasekhar limit is reached "it is generally accepted that a substantial fraction of the carbon and oxygen in the white dwarf is burned into heavier elements within a period of only a few seconds". See the Wikipedia article on Supernovae and the related articles for each specific type for more detail, it's very good and makes it clear that these things are still being debated.

@Benni - It takes a big star to produce iron, and the bigger the star the shorter it lifetime.Really big stars are much less common than smaller stars, so fewer have been observed in spite of their tremendous luminosity. They are also much less stable than smaller stars, and so are much harder to model. Thus we know much less about them.The best estimates for the life span of the biggest stars in our galaxy, such as Eta Carinae, is somewhere around 3 million years. Even larger stars, up to perhaps 300 solar masses, are thought to have existed earlier before the pristine H/He got infused with 'metals'. These would probably have lasted less than 2 million years.

@Benni - It takes a big star to produce iron, and the bigger the star the shorter it lifetime.Really big stars are much less common than smaller stars, so fewer have been observed in spite of their tremendous luminosity. They are also much less stable than smaller stars, and so are much harder to model. Thus we know much less about them.The best estimates for the life span of the biggest stars in our galaxy, such as Eta Carinae, is somewhere around 3 million years. Even larger stars, up to perhaps 300 solar masses, are thought to have existed earlier before the pristine H/He got infused with 'metals'. These would probably have lasted less than 2 million years.

@Real,good post: But now do you see the confusion that was created with the writer of the article inserting seemingly contradictory language? It sounded to me as if old stars (billions of years)exist in a very young infant Universe (a few hundred million), the quotes I made were directly from the article.

@Cal: You're right, I got the two mixed up. I was sure there was one at about 500 million. This brings the redshift at around z=9.2 for 090429B.

Supernovae are caused at the moment iron starts to form in the core. The point I'm trying to make here: this is associated only with extreme aging of stars, a lot older than 520 million years from BB/Inflation. This why I continue to suggest Cosmologists have got to rethink the 13.7 billion year age of BB/Inflation.

Actually, the types of stars that form supernova usually don't live much longer than 10 to 100 million years. Also the term the author used is 'aging' which is relative to the size of the star, not an absolute time scale.

@Benni - the article says 'aging stars', and 'when stars ... come to the end of their lives...'. In an article put out by a university to the public it would have been good at that point to mention that such massive stars age much faster and only live a few million years.But among people who follow astronomy it is pretty well known that big stars burn their fuel so fast that they live short lives while the smallest stars nurse their fuel and live far longer than our sun, so in an astronomy magazine this would be unnecessary, and there are often strict word-count limits.So my bet is that the article popularizes an astronomy paper where the original audience knew about stellar lifespans, and the popularizer didn't see what was missing for a broader audience.In any case, now you know about stellar lifespans.

Big stars shine REALLY bright as they burn through their fuel, which is why they can be seen from so far away.

Can't express how pleased I've been with the helpfulness of your responses. RealScience, your point about the "...broader audience" is why I started this thread with the statement: "I must be more of an amateur than I thought", I suspected the writer may have been making a point about "age" that I was somehow missing, and when @ant phy linked me to that chart was when the final connection was made.

Now, at next month's astronomy club meeting we can we can look at these GRB's & HUDF-JD2 in a less mysterious light.

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